Sedimentation tank



Aug. 20, 1940. N. B. LUND SEDIMENTATION TANK Original Filed Nov. 23, 1935 5 Sheets-Sheet 2 ATTORNEY.

Aug. 20. 1940. N. B. LUND ,5

' SEDIHENTATION TANK I ori inal Filed Nov. 23, 19:5 5 Sheets-Sheet s ATTORNEY.

Aug. 20, 1940. B, LUND Re. 21,536

SEDIMENTATI 0N TANK Original Filed Nov. 25, 1935 5 Sheets-Sheet 4 IHIIIIHI 1, a FIG .8.

Fl G.9

INVENTOR.

NELS B.LUND F l 6 .I4-. BY Owtwn.

ATTORNEY.

Aug. 20. 1940. N. B. LUND SEDIMENTATION TANK Original Filed Nov. 23, 1935 5 Sheets-Sheet 5 NELS B. LUND ATTORNEI.

Reissued Aug. 20, 1940 UNITED STATES PATENT OFFICE SEDIMENTATION TANK Delaware Original No. 2,134,524, dated October 25, 1938,

Serial No. 51;193, November 23, 1935. Applica- I tion for reissue April 16, 1940, Serial No.

5 Claims.

This invention relates to sedimentation tanks and more particularly to improvements in sludge removal and withdrawal means therefor operable during the sedimentation operation.

In tanks of this class a raking or collecting device is rendered eflective by its reciprocating movement to transfer settled sludge over and along the tank bottom to a sludge collection and outlet zone, while clarification or sedimentation continues in the body of liquid in the tank. Conventional practice provides the sludge to be removed by suction.

In the operation of some such sedimentation tanks there are present two contradictory aims, namely on the one hand to reduce as far as possible the time 01 detention of settled sludge in the tank, by substantially immediate removal thereof, and on the other hand the removal of as dense a sludge as possible from the clarified liquid. However, with a body of clear water steadily overlying the settled sludge the desired sludge density cannot be attained unless there is made available a sufllcient sludge accumulation or reserve in the sludge outlet zone, lest the pump should draw an excess of water, and thus water and power losses should accrue aside from the additional difficulty of having to deal with a dilute sludge for disposal of further treatment. It is therefore customary to employ sludge sumps or depressions of various sizes and shapes in which to maintain the required sludge reserve.

Also with the operation of reciprocating sludge raking mechanism especially in rectangular tanks it is necessary to collect an amount of raked sludge directly at and over a relatively constricted sludge suction outlet, so that it has been customary to provide large wide sludge sumps or hoppers incidentally of such a. slope that the sludge received thereby would be sure to gravitate to the vortex or point of sludge suction. Also additional or auxiliary cross conveyors have been used where a reduction of sump size and sludge reserve was to be accepted.

It is one object of the invention to reduce or eliminate the necessity for sump requirements or cross conveyors without foregoing the advantage of having available a desired sludge density at the sludge outlet. In other words, the object is to reduce the expense and labor for excavation and structure, and to reduce total tank depth especially where unfavorable ground water conditlons prevail. r

. Another object is to reduce to a minimum the time of sludge detention in the tank as far as is compatible with a desired sludge density, by reducing the amount of necessary sludge reserve.

Another object is to devise means whereby plain, substantially flat-bottomed tanks having no sludge sumps or sludge removal mechanism, can be converted into tanks with mechanical sludge removal adapted for uninterrupted operation without requiring the breaking through of the tank bottom to supply sludge sumps or to make similar structural changes;

Still another object is to devise improved sludge conveying means of the reciprocating type where byscttled sludge is conveyed from all points and from both ends of a rectangular tank bottom to a restricted sludge outlet therein.

Consequently, this invention contemplates to withdraw settled and collected sludge at certain intervals only, and more particularly only during a predetermined periods of relatively greatest sludge density such as occurs upon the arrival of every new sludge load which is pushed towards the outlet zone through the reciprocation of the rakes. More specifically with respect to rectangular tanks it also contemplates the provision of a reciprocating raking mechanism which is eiiective to transfer settled sludge from all points of the tank bottom including the so-called dead corners or areas thereof towards a restricted zone of sludge discharge and without the use of addition cross conveyors.

According to one feature the invention provides that the sludge withdrawal be controlled or timed so as to take place in a predetermined period during the final phase of the sludge carrying stroke of the reciprocating rake device. To this end, the movement of the sludge scraping device may control the functioning of the sludge suction so that sludge withdrawal is allowed to take place only during a predetermined period in which there is available a suitable although temporary sludge reserve in the way of sludge load brought to the sludge outlet by the sludge conveying stroke of the rake device.

In a preferred form of the invention there is provided an improved raking device of the reciprocating type that will convey the settled sludge from all points of a flat bottom in a manner to have it conveyed substantially directly and from all points of the tank bottom to a relatively restricted suction outlet provided in the flat bottom of the tank. In this way, a sludge conveying stroke of the raking device will in its total efiect cause collected sludge to converge upon the restricted outlet and thereby create at and over the outlet a temporary sludge reserve of suitable sludge density. At the same time, sludge withmatically operated to become effective during the final phase oi the sludge conveying stroke, that is to say, during a predetermined period when the sludge reserve is available.

More specifically the raking device comprises a pair of raking elements depending from a reciprocating carriage and which operate in an alternating and counter current fashion and so that they will clear the sludge from the dead corners of the tank as they convey sludge loads from all pointsofthetankbottomtoandintothesiudge 7 outlet. 7

The invention other objects and features of advantage, some of which, with the foregoing, will be set forth in the followingdescription. In the act-301119 7 8 drawings, for the purpose of example, there has been illustrated the best embodiment of the invention now known, but such embodiment is to be regarded as typical only of many possible embodiments and the invention is not to be limited thereto and more specifically the main principle of operation underlying this invention is also applicable to the round type of tank.

In the drawings:

Fig. iisaplanviewofarectangular equipped with sludge-collectingand sludge-discharge timing means;

Fig. 2 is an enlarged partial longitudinal section taken upon Pig. 1 and showing sludge outlet valve as controlled by the sludge-collector carriage with the valve open;

'oftheinitialphaseoithesludgeoutletoperation:

Flgs.9and lilaresimilartoi'lgs.7and8,with the cam control elements positioned in the middle of the sludge-outlet operation:

rigailandmaresimilartoligafland 10, with the cam control elements in a position when the sludge-outlet operation has beencompleted; Figs:13 and 14 are similar to Figs. 11 and 12, with thecamcontrol elementsinapositionto indicate the one-way camming action thereof with respect to thesludge-outlet operation; and Figs.land loare' viewstoshow characteristic phases of carriage and rake operation formoftheinventionisshowninl'lgJ. in connection with arectangular tank I. having side walls II, it, and end walls II, It, and a substantially fiat bottom II, which is shown to be slightly pitched towards one side of the tank (see Fig.3),at whichsideisprovidedasludgeoutlet opening it, through which sludge maybe withdrawn by suction. and whichishereinshown tobeiocatedsubstantiallynearoneendofthe tankandshowntobeclosertothesidewallll thantotheendwalliioi'thetank. Extending along the side wall ll upon the tankbottom,thereisindlcatedasludge-collectdrawal means such as an outlet valve are autoing zone It, along which sludge can be moved in a straight path to the sludge outlet. Between theopening liandtheendwall lithereisprovided a filler portion II to fill in the dead corner which is flanked by side wall II and end wall II, and which filler portion has the sloping faces I. and ll of a pyramid-like body. A feed inlet for the tank Ill may he provided in connection with the end wall I! and an outlet for eiiiuent liquid in connection with the end wall I.

While the actuating means for the sludgeoutlet control may be of any desired type, for instance, in the way of a hydraulically-operated valve mechanism, there is described in the following a valve-operating mechanism based upon purely mechanical action...

it sludge-outlet valve and operating mechanism 'II is shown to include a valve disc 20 carried by a valve rod li,'a valve seat 22, 'a valve yoke 23 for guiding therein the valve rod 2| the valve rod has an adjustable bifurcated top portion N by which the total length of the valve rod can be varied. This bifurcated top portion is pivoted to a rocker arm 25 (see detail-Figs. 4 and 6) fastened upon the free end of a rock shaft II which is journaled in bearings 21 and 28 mounted upon a bracket 29, which is shown to be anchored upon the inner side of the side wall ll of the tank.

The other free end of the rock shaft 26 carries another rocker arm ll, which is of special construction to act as a cam-operated lever for the periodic operation of the sludge-outlet valve.

makes possible the one way action of the camroller, as will be described. I

The extension -38 is resiliently held in a neutral position by a pair of symmetrically-arranged compression springs 35 and it, which are seated in opposedly-arranged cup-shaped portions 31 and 30, which are part of symmetrical portions or II and ll of the stub portion II. By controlling the depression of the cam roller II the sludge outlet can be controlled to function within a desired predetermined period, whereby it is understood that the rocking lever carrying the cam roller 34 must be depressed against the weight of a liquid column which loads down the sludge valve when the tank is in operation.

It is noted that the sludge outlet valve herein shown is located substantially at the level of the fiat bottom, of the tank, and that there is provided no essential transition or sump to lead from the tank into the sludge outlet proper. Nor is there provided a cross conveyor or the like for delivering sludge collected at one end of the tank crosswise to and into the sludge outlet. Consequently, there is herein disclosed a reciproeating sludge-conveying device of improved design, which is to convey the sludge not only lengthwise of the tank, but at the same time in a lateral direction, so that in eiiect the settled sludge is caused to converge from all points of the tank bottom'to the restricted sludge outlet.

It will be understood that the required sludge reserve at the sludge outlet is to be provided by the properly-timed operation of the sludge outlet valve in conjunction with the operation or reciprocation of the sludge-conveying device presently to be described.

Upon the sides of the tank are mounted track rails 41 and 42, upon which operates a carriage 41 spanning the width of the tank, and which comprises a frame 44 supported by track rollers 46. The carriage may be equipped with suitable driving means (not shown) to effect its operation or reciprocation along the tank, that is to say, it may be provided with motor means in the way of a self-propelling carriage, or its movements may be controlled by a rope drive of a suitable kind.

The carriage 43 has depending therefrom two sets of raking elements 46 and 41 (see Fig. 1), which by suitable mechanism (not shown) are controlled to operate in alternating fashion as the carriage reciprocates. The raking element 46, which may hereinafter be called the auxiliary raking element, comprises a series of inclined raking blades 46, which are to be rendered operable when the carriage travels in the direction towards the end wall 14 of the tank and away from the sludge outlet. The other raking element 41, which may hereinafter be called the main or scoop-equipped raking element, comprises a similar, but opposedly-arranged series of inclined raking blades 49, and in addition thereto a scoop member 50, which, in turn, includes a short inclined' blade portion 60* and a long substantially transverse blade portion 60", extending in back of the inclined blades 49 and spaced therefrom as by clearances The raking element 41 is to be rendered operative in alternation with the raking element 46 and during the time the carriage travels toward the end wall It of the tank, and towards the sludge outlet.

The carriage frame 44 is shown to have mounted thereon face-downward a cam rail 6|, which is to effect the timed operation of the sludge outlet valve through one-way operative engagement with the cam roller 34, incident to the reciprocation of the carriage 43. The cam rail 6| may be adjustable relative to the carriage frame in order to determine and adjust the period 'of sludge-valve operation. The cam rail as shown comprises a shallow curved portion 62, which defines the opening phase of the valve, a substantially horizontal portion 63, which marks the phase of maximum valve opening, and a vertical portion 64, marking the closing of the valve.

Figs. 15 and 16 are diagrammatic lateral views of the sludge-collection device in the tank. A carriage frame 66 has hinged thereto and suspended therefromat 66 and 66", respectively, a pair of rake suspension members 66 and 61, arranged in crosswise or intersecting fashion, and carrying respective rake elements 66 and 69. The rake element 66 corresponds in effect to the auxiliary raking element 46, and the rake element 66 to the main or scoop-equipped rake element 41 of Fig. 1. A sludge outlet is shown at 62, whereas the showing of the sludge discharge control mechanism is not repeated in Figures 15 and 16. The rake elements, through mechanism not shown, are operable in alternating fashion in such a manner that the one is swung up to inoperative position when the other one is lowered to operate upon the tank bottom.

The operation of the sludge-collecting and the sludge-withdrawal means will now be described.

With reference to Fig. l, the carriage 43 may be assumed to be on its way towards the end wall I! of the tank Ill and towards the sludge outlet of the tank as indicated by arrows. Through suitable mechanism, not shown, provision is made so that at the time, the scoop-equipped raking element 41 is actively engaged in moving sludge over and along the major portion of the tank bottom in the direction of the end wall I! and towards the sludge outlet 62. While traveling over the tank bottom, this raking element plows the sludgein a compound movement forwardly and laterally of direction of rake movement as a result of the action of the inclined raking blades 46 and also due to the effect of the slope'of the tank bottom it. The slope of the tank bottom It is further conducive to produce movement of the sludge in lateral direction as the sludge is intercepted by the transverse blade portion 66 of thescoop-member 56 when the sludge leaving the trailing end of the raking blades 49 passes gradually through the clearances .towards the side wall II and into the collecting zone l6 therealong, from which zone it is conveyed substantially directly to the sludge outlet l6 by the scoop member 50 as a whole.

The sludge thus conveyed by the plowing action of the inclined blades 48 in combination with the positive action of the scoop member 60, will provide the required sludge reserve for the sludge withdrawal or sludge suction period during the final phase of this operating stroke of the raking element 41.

The period of sludge withdrawal and the operation of the control mechanism therefor will be more clearly described below. However, it should be clear that after the sludge outlet valve mechanism has been operated and the valve will have been closed, the carriage will have reached its terminal position at the end wall l4 of the tank. The movement of the carriage may then be reversed automatically or otherwise, and along with such reversal some suitable mechanism (not shown) may operate to render inoperative the main raking element 41, while causing the auxiliary raking element 46 to engage upon the sludge deposited in the .dead bottom area between the sludge-outlet opening l6 and the end wall I4 of the tank. The rake element 46 which differs by its lack of a scoop element from the main raking element 41, will now operate to bring sludge from the dead area into the operating range of the rake element 41, and in this way sludge from dead areas or corners will ultimately be delivered to and into the sludge-outlet opening I6 as the cycle of carriage reciprocation continues.

The auxiliary raking element 46 may continue operative over and along the tank bottom until the carriage reaches the other end wall 14 of the tank, during which trip away from the sludge outlet this raking element 46 is effective to impart to the sludge a composite movement which is slightly away from the sludge outlet but essentially laterally towards the side wall H of the tank, thus contributing to a desired total lateral movement of the sludge, and assisting the main raking element 41 in its tendency to collect sludge in the longitudinal marginal zone along the side wall II and ultimately to the sludge outlet.

. With respect to the function of the sludge valve proper, it is clear from the drawings that the period of sludge-valve operation during the final phase of the operating stroke of the main raking element 41 is controlled by the engagement of the cam rail 6| upon the cam roller 34. That is to say, as the carriage approaches the end wall 13 of the tank, the curved portion 52 of the cam rail engages upon the cam roller 84 depressing the same and the rocker arm 8| and lifting-the valve rod 2| and the valve disc 20, unseating it as against the static pressure of the overlying liquid in the tank. During further progress of the carriage at a predetermined rate of speed the cam roller 14 will ride along the horizontal portion II of thecam rail, the length of which determines the period of maximum valve opening to be made available for sludge withdrawal and which is so determined that preferably the volume withdrawn will not exceed the volume of suitable sludge available at the valve outlet.

It is noted that the cam rail II is set at a slight angle relative to the direction of carriage movement (see detail-Figs. 8, l0, l2 and 14) so that, as the cam roller 34 follows the guidance oi the cam rail, the extension II correspondingly assumes a slightly angular position relative to its neutral line, until the cam roller reaches the vertical terminal portion 54 of the cam rail ll. At this time the cam roller 84 will leave the cam rail somewhat abrup y. unless snubbed, to permit the closing of the sludge valve which will promptly occur as a result of hydraulic static pressure acting upon the valve disc, and also to permit the-extension 33 to return to neutral position from its angular displacement, and in so doing to escape or dodge the cam rail when subsequently the movement of the carriage is reversed. This means that aftercarriage reversal the sludge valve remains -closed, only to open again whenever the. main raking element 41 returns with a new sludge load to furnish a temporary sludge reserve.

The operating cycle of the sludge-collecting and discharge mechanism is furthermore diagrammatically illustrated in Figures 15 and 16, and the respective characteristic operating positions of the sludge-collecting device are designated by the letters A, B, C and D.

When the carriage has reached the position A at the end of a stroke directed away from the sludge outlet 62. the auxiliary rake element II is lifted or swung about the pivot It" as indicated by arrows pointing upwardly, while the scoopequipped element It is lowered or swung about pivot 55' to the tank bottom, as indicated by the arrows pointing downwardly. With the rake element 59 now rendered operative, the carriage it travels towards the sludge outlet 82 according to the position B (shown in dotted lines) of the carriage and the horizontal arrows pointing in that direction, the scoop of that rake element then being effected in apositive manner to convey a sludge load to the outlet 82. where it is withdrawn or sucked away during a predetermined period as previously described.

Thereafter (see position C in Fig. 16) the scoopequipped rake element 58 is lifted in the upward direction of the arows shown, while the auxiliary rake element 68 is lowered (note the downward arrows). The carriage then starts on its return trip away from the sludge outlet 62 with the sludge outlet closed and the auxiliary rake element Bl operative as previously described, whereby the sludge is plowed in a substantially lateral direction without being advanced in a positive manner as it would be by the scoopequipped raking element 59. This phase of the operating cycle is indicated by the position D (shown in dot and dash) of the carriage and in the showing of the horizontal arrows attached thereto.

a1,sso

I claim:

1. In combination with a rectangular sedimentation tank having side and end walls, a substantially flat bottom, and a relatively restricted sludge outlet adjacent the near end of the tank as distinguished from the opposite end of the tank and which outlet is narrower than the width 01 the tank; a settled sludge conveying and collecting device comprising a carriage operable in reciprocating fashion along the tank, a main sludge impelling and conveying element and an auxiliary sludge impelling element, both elements depending from said carriage, means for shifting each sludge impelling element in alteration with the other from a lower sludge engaging position to an upper idle position and vice versa to efl'ect operation of said elements alternately countercurrent to one another from the respective ends of the tank, said main sludge impelling and conveying element comprising a scoop element eflective to convey sludge from said far end of the tank along a direct path of action towards and into said outlet, and inclined sludge engaging blade means cooperatively associated with said scoop element and effective to transfer sludge laterally of the direction of the carrage imovement into said path of action of the scoop element, said auxiliary sludge impelling member comprising a series of sludge engaging blades inclined in a direction opposite to that in which the main sludge impelling blade means are inclined and substantially effective to convey settled sludge from said near end of the tank into the path of movement of the main sludge impelling and conveying member; and track means for operatively supporting said carriage with respect to the tank.

2. In combination with a rectangular tank having side and end walls, a laterally sloping relatively flat bottom, and a restricted sludge outlet located at the lower portion of the slope, a carriage operable in reciprocating fashion along the tank, a pair of sludge impelling members depending from said carriage, means for shifting each sludge impelling member in alternation with the other from a lower sludge engaging position to an upper idle position and vice versa to effect operation of said members alternately countercurrent to one another from the respective ends of the tank, one of said members comprising inclined blade means eilective to impel settled sludge in a direction laterally from the direction of carriage movement, and a scoop element spaced from the trailing end portion of said inclined blade means and arranged to intercept sludge therefrom, and adapted for conveying the intercepted sludge substantially directly to said sludge outlet. said scoop element comprising a blade portion extending substantially transversely across the tank bottom area covered by said inclined raking blade means, the intercepted sludge being urged along said blade portion and down said slope, the other of said pair of members comprising means for transferring sludge into the path of movement of said one of said members; and track means for operatively supporting said carriage with respect to the tank.

3. In combination with a rectangular sedimentation tank having side and ends walls, a substantially flat bottom, a relatively restricted sludge outlet adjacent the near end of the tank as distinguished from the opposite far end of the tank and which outlet is narrower than the width oi the tank; means for controlling the discharge of the sludge through the outlet; a settled solids I sues conveying and collecting device comprising a carriage operable in reciprocating fashion along the tank, a main sludge impelling and conveying member and an auxiliary sludge impelling member, both members depending from said carriage, means for shifting each sludge impelling member in alternation with the other from a lower sludge engaging position to an upper idle position and vice versa to effect operation of said members alternately countercurrent to one another i'rom the respective ends of the tank, said main sludge impelling. and conveying member comprising a scoop element effective to convey a sludge load periodically and incident to the reciprocation of the element from said far end of the tank along a direct path of action towards and into said outlet, and inclined sludge engaging blade means cooperatively associated with said scoop element and eil'ective to transfer sludge laterally oi! the direction of the carriage movement into said path of action of the scoop element, said auxiliary sludge impelling member comprising a series of sludge engaging blades inclined in a direction opposite to that in which the main sludge impelling blade means are inclined and substantially efl'ective to convey settled sludge from said near end of the tank into the path of movement of the main sludge impelling and conveying member; track means for operatively supporting said carriage with respect to the tank; and means connected with the carriage for actuating said sludge control means and for eti'ecting sludge discharge during a period substantially coincidental with the arrival of a sludge load at said outlet conveyed thereto by said scoop element.

4. In combination with a rectangular sedimentation tank having side and end walls, a substantially flat bottom, a relatively restricted sludge outlet which is narrower than the width of the tank; means for controlling the discharge of the sludge through the said outlet; a settled sludge conveying and collecting device comprising a carriage operable in reciprocating fashion along the tank, a pair oi sludge impelling members depending from said carriage, means for shifting each sludge impelling member in alternation with the other from a lower sludge engaging position to an upper idle position and vice versa to eiiect operation of said members alternately countercurrent to one another from the respective ends oi the tank, one of said sludge impelling members comprising a scoop element effective to convey a sludge load periodically and incident to the reciprocation of the element from one end of the tank along a direct path or action to and into said sludge outlet, and inclined sludge engaging blade means cooperatively associated with said scoop element and effective to transfer sludge laterally of the direction of the carriage movement into said path of action of the scoop element, the other of said pair of members comprising means for transferring sludge into the path or movement 01' said one of said members, track means for operatively supporting said carriage with respect to the tank, and means connected with the carriage for actuating said sludge control means and for eilecting sludge discharge during a period substantially coincidental with the arrival of a sludge load at said outlet conveyed thereto by said scoop element.

5. A sedimentation tank according to claim 4,

in which the outlet is located adjacent aside wall of the tank, and. in which the direct path of action of the scoop element is accordingly also located adjacent to said side wall. 

